The goal of these studies is to increase understanding of the diagnostic, therapeutic and pathogenic aspects of parasitic infections. Work with hemlminth infections has identified species specific antigens as well as particular types of antibody responses (IgE and individual IgG subclasses) that show enhanced specificity in the diagnosis of filariasis, schistosomiasis and strongyloidiasis. Sensitive diagnostic methods for detecting parasite antigens circulating in the blood (filariasis, schistosomiasis) or found in th stool (giardiasis) have also been developed. Therapeutic studies of patients with cutaneous leishmaniasis indicate that local heat treatment for isolated lesions is effective in selected cases. Long-term studies of the efficacy of diethylcarbamazine (DEC) used prophylactically (loiasis) or chronically (bancroftian filariasis) either with or without other drugs are underway in Africa and India. The violent side effects of DEC treatment in patients with onchocerciasis appear to be initiated by complement activation that leads to destruction of microfilariae followed by widespread immediate hypersensitivity reactions. The pathology of parasitic infections results from both the patient's immune responses to the parasite and the pathogenic potential of the parasite itself. For helminth infections (filariasis, schistosomiasis, strongyloidiasis) cellular and humoral (especially IgE) immune responses and their specific regulatory mechanisms have been characterized. Work on the pathogenicity of protozoal infections (giardiasis, leishmaniasis) has focused more on strain differences among the parasites and their roles in determining both the character of the pathology induced in patients and the clinical response of these patients to treatment.